(a) Field of the Invention
This invention relates to apparatus for connecting pipes or the like. More specifically, apparatus of this invention is for connecting pipe or the like capable of being connected and disconnected quickly and frequently under difficult conditions.
(B) Description of the Prior Art
In the offshore pipeline construction industry, pipe lines are laid in subsea locations by streaming the same from the after end of lay barges as the lay barges are propelled forwardly through the water. To support the pipe during its movement from the deck of the lay barge into the water, lay barges are provided with rearwardly extending buoyant ramps known as stingers. When laying large diameter pipe in deep water, it is desirable to use a longer stinger than is used with small diameter pipe in shallow water. However, rather than fit the lay barge with several interchangeable stingers of various lengths, it is desirable to provide buoyant extensions which may be connected to and disconnected from the stinger as conditions change. It is therefore necessary that a connector or system of connectors be provided.
One type of connector which has great strength and rigidity, and therefore is potentially well suited for use as a connector for stinger extensions, is the type in which a plurality of self-locking cams carried by one part of the connector engage a radially outwardly extending flange of the other portion of the connector in self-locking fashion. By self-locking is meant that the angle of taper of the cams is such that the cams will remain in engagement with the flange until a retracting force is applied thereto. (This is analogous to a nut on a bolt. The nut exerts an axial force when torque is applied thereto, but when the torque is removed, the nut stays in place.) There are, however, several disadvantages associated with using a connector of the self-locking cam type.
First, the coupling of such connectors is slow. It takes a rather substantial amount of time to seat the cams against the flange, and because the connection would be made in an offshore location where the stinger and extension would be subject to wave action, the connector would be extremely vulnerable to damage during the coupling thereof.
The vulnerability to damage of such connectors is even greater during break-away. Because the self-locking properties of the cams are functions of both the angle of their taper and of the coefficient of friction between the cam surface and the flange, each cam has slightly different properties and therefore each cam requires a different amount of force to retract it from the engaged position. Since the cams are actuated by a single hydraulic system, the tendency is for the cams to unseat randomly, with cams having lower self-locking properties unseating and retracting first while the other cams remain engaged. Consequently, each of the remaining cams is forced to share a greater load, which increases the possibility of damage to the connector by the shearing off of cams. Further, if one connector releases before another, structural damage to the extension and stinger becomes likely.